Earnings per Share - Additional Information (Detail) (USD $)	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase shares of common stock, incremental shares excluded from the computation of diluted EPS	3,169,055	994,730
Options to purchase shares of common stock, weighted average exercise price of incremental shares excluded from the computation of diluted EPS	$ 65.57	$ 67.34

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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+ Details